A little more research indicates the image is from the Byron Collection of the Museum of the City of New York. From the museum's website on the collection:
This database contains digital images and descriptive information about individual works in the Byron Collection. The collection consists of over 22,000 photographs of New York City and its environs taken by the Byron Company between 1890 and 1942.
If you run a search on 'keith' and 'bicycle' in their online database, a series of four images come up, all taken of the same bicycle track- http://museumofnyc.doetech.net/wiz10.cfm
If you just search on the term 'bicycle' there are actually a number of other stunt and trick bicycle images that are returned. So I'd say in the broader context of a known collection maintained by a museum that the image is 100% authentic.
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